Cape Bay scallops aren't available anywhere this time of year. The season runs from late October to early spring. Never seen them in the shell myself but you could try Joe's Lobster Mart on the canal in Sandwich. IMO it's the best fish market on the entire Cape by a mile.

The episode you refer to was just aired again tonight. Very interesting! Essentially a Cape Bay scallop grown in Buzzards Bay but no restriction on the season as Chatham Bars Inn features them as a special menu item on Fridays. They get them fresh that day. Plus, they say you can eat the whole scallop, not just the 'muscle' as they're grown in cages so there's no sand. Please post if you find them anywhere. As a plus, they look really beautiful, I'd like to experiment with them.